This application claims benefit of Japanese Patent Application No. 2002-345651 filed on Nov 28, 2002, the contents of which are incorporated by reference.
The present invention relates to wireless LAN (local area network) systems and, more particularly wireless LAN systems, in which such hosts as PC (personal computer) or PDA (personal digital assistant) or the like is interconnected for inter-host communication, such as reception of IP phone calls (i.e., made by transmitting voice signals in packets based on an internet protocol) and electronic mail.
It has been proposed to interconnect such hosts as PC and PDA via a wireless LAN instead of a wired communication line such as a telephone line. The use of the wireless LAN has various merits such that hosts are not installed in fixed places but can be freely moved to any desired place, if necessary, and also that the hosts can be interconnected without need of any wiring. In each of such hosts interconnected by the wireless LAN, a wireless LAN device is mounted.
In the meantime, the operation of the above host, however, dictates considerable power consumption. The total consumed power thus increases in proportion to the number of hosts. This consumed power can not be ignored, and in the case of a host which is driven by a built-in battery or the like high consumed power is undesired. As for the user side, the host is not always in use, and mails or the like are not always arrived.
The power supply of the host is usually held “off” while the user does not use the host or when the user has not used the host for a predetermined constant period of time to reduce the power consumed in the host. As a different prior art, a LAN circuit system or the like has been proposed, which causes, in a LAN, a mode shift to a sleep mode, in which a node is held in a passive state for a predetermined period of time, for consumed power reduction, and also causes wake-up upon detection of a signal transfer start signal from the network side in an edge detection circuit or the like (see Literature 1: Japanese Patent Laid-open Hei 6-303242).
A prior art as shown has a problem that by turning off the power supply of a host connected to an associated wireless LAN device the power supply thereof is also turned off. At this time, an arrival of an IP phone or a mail as noted above, if any, from another host could not be received. In other words, any arrived IP phone or mail could not be received unless the power supply of the wireless LAN device is turned on in the “on” state of the power supply of the host.